I am no cattle expert by any means.

I did have some experience in this area last spring. I had a larger heifer who had hooves showing out the back of her on Sunday morning when I checked. I went to church figuring I'd have a calf when I got back.

Back from church, still just hooves. She was not in any visible/unusual distress, just walking around with hooves visible out the back.  Walked back from pasture to the phone. Called a neighbor for advice, he seemed very concerned - quoted the one hour rule also. He said to call the vet for an opinion. Called vet. Left message. He called me back in 1/2 hr or so...now going on 3 hrs. He seemed concerned also. Now I am getting concerned.

He said he had another calving emergency and would come over as soon as he could. Now its going on 4 hours since I saw the hooves. Who knows how much before that they were first showing.

Walked back out to the pasture. There she was licking off what turned out to be the biggest calf of the spring bunch. A beautiful big bull calf. Everything was just fine.

I called the vet back to cancel his visit and he said that a first calf heifer with a big calf may just take longer. He said try to let nature take its course, unless she is down and seems in distress. He said sometimes by trying to help to soon you can cause  more problems than you solve. His quote.

This may or may not be appropriate for your situation. We have to be careful about medical/vet advice on the internet - your vet is the best source. The one hour rule may be common but there may also be times for exceptions. FWIW. Good luck.

Jim at Dawn